Controlling the treatment of fibrous material

ABSTRACT

A method for controlling a device for treating a fibrous material includes the steps of: providing that the device includes a housing in which at least a first treatment tool and a second treatment tool are arranged; mounting at least one of the first base plate and the second base plate in an axially movable manner in order to compensate for a wear of the first treatment profile and the second treatment profile; measuring a distance between the first base plate and the second base plate respectively of the first treatment tool and the second treatment tool of a treatment nip during an operation of the device; and selecting a value of a total power depending on the distance between the first base plate and the second base plate of the at least one treatment nip.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application no. PCT/EP2021/076575,entitled “CONTROLLING THE TREATMENT OF FIBROUS MATERIAL”, filed Sep. 28,2021, which is incorporated herein by reference. PCT application no.PCT/EP2021/076575 claims priority to German patent application no. DE 102020 125 487.3, filed Sep. 30, 2020, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method for controlling a device forthe treatment of fibrous material, wherein the device includes ahousing, in which at least one first treatment tool and a secondtreatment tool are arranged. The treatment tools respectively aremounted on a base plate and have a rotationally symmetrical shape andare arranged coaxially to each other, rotating relative to one anotherabout a common axis. The treatment tools delimit a treatment nip throughwhich the fibrous material flows and respectively have a treatmentprofile which faces toward the treatment nip, wherein at least one baseplate of a treatment tool is mounted in an axially movable manner inorder to compensate for the wear of the treatment profile.

2. Description of the Related Art

Because of the relatively high consistency of the fibrous materialduring treatment, intensive mechanical processing with equipment of thistype (refiner, disperger, deflaker) is possible, even though thetreatment tools which move relative toward one another do not makecontact with each other, but rather pass each other at a relativelysmall distance, whereby considerable forces occur. Devices of theaforementioned type are used, for example, to improve the quality ofpulp, TMP or fibrous material obtained from waste paper.

It has been known for a long time to refine pulp fibers, that is virginpulp and/or waste paper fibers, in order to be able to obtain thedesired characteristics in the therefrom produced fibrous web, inparticular in regard to strength, porosity, formation and surface.

In the refiners used for this purpose, the refining surfaces areprovided by replaceable refiner fillings which – because of therelatively rapid wear – are screwed to the corresponding base plate.

In order to achieve the desired fiber characteristics, in particular thedegree of refining, the refiner fillings have to be optimally adapted tothe fibers to be treated, also to prevent excessive wear of thefillings.

In addition, optimum use of the available refining surface is strivedfor in order to increase efficiency of the fiber treatment.

From US 2004/0112 997 A1 as well as DE 2 939 587 A1 and DE 3 602 833 A1it is known to measure or calculate the no-load power once beforestart-up and to use it as a basis for the machine control.

If the height of the treatment profile of the treatment tools is reduceddue to wear, this leads to a reduction in the no-load power orrespectively the pump power. With constant total power, this also leadsat the same time to an increase in the specific power of the device thatis relevant for the desired treatment intensity and thus to excessivetreatment, in particular refining of the fibers. Constant total power isthereby regulated by axial displacement of the axially movable baseplate.

In turn, if the nip is too small, there is a risk of excessiveelectrical current consumption and contact between the treatment tools.

From DE 10 2016 207 726 A1 it is known to determine the no-load powerduring operation. For this purpose, however, it is necessary to operatethe refiner in no-load mode or to flood it with water and to open andclose the treatment nip while measuring the no-load power. The thusmeasured no-load power is then used as a basis for further operation.

What is needed in the art is to make possible a reliable and efficientoperation of these devices by the simplest possible ways.

SUMMARY OF THE INVENTION

The present invention relates to a method for controlling a device forthe treatment of fibrous material, wherein the device includes ahousing, in which at least one first treatment tool and a secondtreatment tool are arranged. The treatment tools respectively aremounted on a base plate and have a rotationally symmetrical shape andare arranged coaxially to each other, rotating relative to one anotherabout a common axis. The treatment tools delimit a treatment nip throughwhich the fibrous material flows and respectively have a treatmentprofile which faces toward the treatment nip, wherein at least one baseplate of a treatment tool is mounted in an axially movable manner inorder to compensate for the wear of the treatment profile. Foradjustment of the total power the width of the treatment nip is adjusteduntil the predetermined total power is achieved.

The present invention provides that the distance between the base platesof the treatment tools of a treatment nip is changed during operation ofthe device for controlling the total power, and the value of the totalpower is therein selected depending on the measured distance between thebase plates of the treatment nip. The measured distance is understood,in particular, to also represent a change in distance originating froman initial value. On the one hand, the distance can be measured directlyin that the distance of, for example, the treatment tools or of the baseplates on which the treatment tools are mounted is measured. However,the distance can also be measured indirectly. In one embodiment, forexample, the position of the drive for tracking the axially movableplate of the treatment tool can be concluded from the change indistance.

Since the no-load power of the device decreases relatively significantlyduring the duration of operation of the treatment tools with increasingwear of the profile of the treatment tools, the total power whichincludes the no-load or pump power and the specific power that isrelevant to the strived for treatment intensity must be adjustedaccordingly. In this way, an unintended increase in the specific powerand thus also of the treatment intensity of the fibers can effectivelybe countered.

This becomes possible in particular, because the general width of thetreatment nip is many times smaller than the profile height of thetreatment tools. Thus the width of the treatment nip can be neglected inthe control unit. With fiber suspension supplied, the formation of atreatment nip is achieved in operation and a treatment nip width is setuntil a predetermined total power is achieved. Since the nip width ofthe treatment nip is negligible compared to the profile height, thevariation of the nip width of the treatment nip – whereby the treatmentnip width can also be dependent on the throughput – is therefore alsonegligible compared to the change in position due to the wear of thefillings. From the measured distance/change in distance the profileheight or, starting from an initial value, a change in the profileheight can thus be determined. In a device having one treatment nip theprofile height corresponds to half the distance between the base plates;and in a device having two treatment nips, the profile height, afterdeduction of the width justified by non-profile components, is a quarterof the determined distance value. It is also possible, starting from aninitial distance value, to determine the reduction of the distance bymeasurement and from this to determine directly the reduction of theprofile heights. Depending on the determined profile height and thetreatment intensity, the relevant total power is set.

One design variation provides that the wear of each filling rounded to0.1 mm, optionally rounded to 0.5 mm, is indicated. A displacementsensor or also an incremental encoder can be used as a sensors fordetermining the position or the change in position.

In order to simplify the control, the value of the total power should beselected solely depending on the measured distance between the baseplates of the treatment nip or in connection with the desired refiningenergy. The measured distance corresponds thereby to the determinationof the profile height. Optionally, the ratio of profile height and thetherewith associated no-load power is stored in a characteristicdiagram. The characteristic diagram can be read in by the operatorbefore start-up or can also have been provided by the manufacturer ofthe device. This means that it is not necessary to determine the no-loadpower during operation.

In an optional embodiment it is provided that the rotor in a devicehaving a double nip is mounted in a floating manner. This means that thedistance between the treatment tools can be adjusted corresponding tothe height of the profiles for both nips by way of an axially movabletreatment tool.

A more precise control is possible if the value of the total power isselected by considering additional values such as flow and stockconsistency and/or the quality of the fibrous stock suspension.

It is advantageous to adjust the value of the total power at least whena change in distance between the base plates of the treatment nip of atleast 1 mm is detected. This corresponds to a reduction of eachtreatment profile of 0.5 mm at a treatment nip.

However, it is often sufficient if the value of the total power isreselected at predetermined time intervals at a maximum of once a day,optionally at least once a week, depending on the measured change in thedistance between the base plates of the treatment nip. Between thesetime intervals, the distance between the base plates is reducedaccording to the wear of the treatment profile in order to keep thetotal power constant at the current value.

When controlling or regulating the device, the no-load power, whichrelates to the throughput of fibrous material per unit of time andwhich, in refiners, is for example usually between 40 and 250, inparticular between 40 and 150 kWh per ton of dry weight, should also betaken into account if possible.

After an intervention in the device, i.e. by replacing only part of thefillings, a distance value measured during opening and/or closing of thetreatment nip can be used once as a new starting value of a no-loadpower for establishing a reference to a stored characteristic diagram.In the subsequent control of the total power, in addition to thedistance value, further links with other parameter values can be used tocontrol the total power and thus also the specific power of the device.

Provisions can moreover be made to measure the no-load power each timebefore the refiner is shut down. Furthermore it can be providedadditionally or alternatively that a determination of the no-load poweris only made after a predetermined minimum operating time. This preventsthe no-load power from being determined every time the device isstopped, several times a day. A no-load determination every 1 to 2 weeksis completely sufficient due to the stored characteristic diagrams and acorresponding tracking of the total power. This reliably prevents anundesirably high refining power.

It has hitherto been customary to determine the no-load power of thedevice at start up and to store it for the control system or to use apredefined value for this purpose.

With increasing operating time of the respective treatment tools andthus also increasing wear of the latter, in particular of theirprofiles, the current no load power of the device decreases. As aresult, the total power consumption would have to be reducedaccordingly.

However, since the no-load power is regarded as constant in previouscontrol systems, the total power consumed may be 20% or more too highfor the desired treatment intensity.

In order to be able to store a start value for the controller in thememory after replacement of at least one treatment tool, it can beadvantageous to have the no-load power measured and entered by theservice personnel or to have the no-load power measured by thecontroller itself, in particular when closing the treatment nip.

Irrespective of this, the value of the total power for controlling thedevice should be selected in such a way that the specific power of thedevice relevant for the desired treatment intensity, which results fromthe difference between the total power and the no-load power, isconstant over the operating period. In this way, constant treatmentintensity can be ensured. The specific power is considered constant ifthe specific power deviates by less than 5% from its arithmetic averagevalue.

If the redetermination of the value of the total power is not carriedout continuously but at certain time intervals, the length of these timeintervals must be selected in such a way that possible changes due towear of the processing profile are tolerable with regard to the thenincreasing specific power. A change of less than 5% of the last assumedno-load power and/or a position change of less than 1 mm per nip isconsidered tolerable.

When determining the value of the total power subject to the distancebetween the base plates of the treatment nip, it is advantageous torefer to values stored in a memory of the control system, in particularto a characteristic diagram. The stored values or the characteristicdiagram were specified by the manufacturer of the device or determinedin advance by the operator of the device during tests.

The values stored in the memory are based on knowledge or experienceregarding the no-load power with the corresponding distance between thetwo base plates of the treatment nip and related to this, also on thedegree of wear of the treatment profiles. Taking into account thedesired treatment intensity of the fibers and thereby the specificpower, this results in the specified value for the total power of thecontroller as a sum.

In the interest of a simple design of the device, one treatment toolshould rotate and the other should not, with at least one treatment toolbeing mounted so as to be axially movable.

In special designs, the treatment tool and base plate can also be madein one piece.

It is also possible for the housing to have several, in particular twoparallel treatment nips arranged next to one another, optionally eachwith one treatment tool rotating on a shaft, and one non-rotatingtreatment tool. As a rule, the two treatment tools respectively adjacentto the other treatment nip are mounted on a common base plate, whereinthis common base plate and at least one of the treatment tools notmounted on this base plate are mounted in an axially movable manner.

The application of the method according to the present invention isespecially advantageous in a refiner, in particular an LC(low-consistency) refiner, wherein the consistency of the pulp isbetween 2 and 6, optionally between 3.5 and 4.5% of the dry weight.

Fibrous material can in particular also be TMP, high-yield cellulose,MDF (medium-density fireboard) fibrous material, wood chips or similarsubstances.

The present invention is explained in more detail below with referenceto an exemplary design example.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of at least one embodiment of the invention taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic cross section through a refiner; and

FIG. 2 is the change in no-load power P_(L) and the adjustment of thetotal power PG over time t and over the distance s between base plates7,8.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate at least one embodiment of the invention, and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

According to FIG. 1 , fibrous material 1 is pressed directly into thecentral, that is the radially inner, region of the refiner fillings,which is formed by the two treatment tools 3,4.

While one treatment tool 3 is fixed and is thus designed as a stator,the other treatment tool 4 is rotatably mounted in housing 2 of therefiner.

Treatment tools 3,4 each have a rotationally symmetrical shape, wherebythe two circular refining surfaces are arranged parallel to one another.Treatment nip 6 between the refining surfaces is adapted via an axialmovement in order to achieve a predetermined total power. The treatmentintensity of fibrous material 1 – also referred to as fibrous suspension–flowing into the nip is established by the nip width of treatment nip6. The axial extent of said nip width of treatment nip 6 is negligiblein comparison with the height of treatment profiles 9 of treatment tools3, 4.

Rotating refining surface 9 is herein moved in the direction of rotationby a shaft rotatably mounted in housing 2. This shaft is driven by adrive, also provided in housing 2. In the illustrated example, fibroussuspension 1 passes via an inlet through the center into treatment nip 6between the refining surfaces of both treatment tools 3,4.

Fibrous suspension 1 passes the interacting refining surfaces in aradially outward direction and exits the adjoining annular space throughan outlet.

Both refining surfaces are formed respectively by several refiningplates, each of which extends over a peripheral segment of thecorresponding refining surface. Arranged side-by-side in peripheraldirection, the refining plates provide a continuous refining surface.

The refining plates and thereby also the refining surfaces have atreatment profile 9, facing toward treatment nip 6, wherein said profileis generally formed by a multitude of essentially radially progressingrefining bars and grooves between them.

The already known ways with which non-rotating treatment tool 3 isaxially moved is not shown. The extent of this axial movement ismeasured by a displacement sensor. Rotating treatment tool 4 does notchange its axial position.

It can also be measured by way of an incremental encoder on the drivefor setting the axial position of the non-rotating but axially movabletreatment tool 3 (not shown).

Furthermore, treatment tools 3,4 are attached to corresponding baseplates 7,8.

In contrast to the example shown here, treatment nip 6 can progress notonly perpendicular, but also – as in the case with cone-refiners –inclined toward axis of rotation 5. In addition, housing 2 can alsoinclude several, in particular two treatment nips 6.

FIG. 2 illustrates the change in the real no-load power P_(L) of therefiner over distance S, which decreases with increasing operating timet and thereby also with increasing wear of treatment profile 9 oftreatment tools 3,4.

The total power P_(G), which is supplied to the treatment deviceconsists of the no-load power P_(L) and the specific power P_(S)responsible for the treatment intensity, that is the refining power offibrous material 1.

The total power is set to a predetermined value that corresponds to thedesired treatment intensity at a known no-load power. In order to avoidthat the specific power Ps becomes significantly higher over the servicelife of treatment tools 3, 4 than would be required for the desiredtreatment intensity of fibrous material 1, the assumed no-load powerP_(L) is adapted accordingly depending on measured distance s betweenbase plates 7, 8 and/or the distance between treatment tools 3,4 byaccessing the stored values or the stored characteristics diagram.

By changing the distance s between base plates 7,8 of treatment tools3,4 of treatment nip 6 during operation, the total power P_(G) consumedby the device can be controlled easily and efficiently. It is essentialto the present invention that the value of the total power P_(G) isselected depending on distance s between base plates 7,8 of treatmentnip 6.

The value of total power P_(G) is herein optionally chosen so that thespecific power Ps of the device, which is relevant for the desiredtreatment intensity, is as constant as possible over the operating time.

When selecting the value of total power P depending on distance sbetween base plates 7,8 of treatment nip 6, values stored in the memoryof the controller are accessed which are specified by the manufacturerof the device or were determined by the operator of the device duringtests.

The value of total power P specified for the control of the device canbe continuously adapted to distance s between base plates 7,8 oftreatment nip 6, as shown in FIG. 2 as a dashed line.

Alternatively, according to the solid line for total power P_(G) in FIG.2 , it is also possible to readjust the value of total power P_(G) todistance s between base plates 7,8 of treatment nip 6 at certain timeintervals. Alternatively it may also be provided that the total power isadapted depending on change s. The adaptation is based on the no-loadpower assigned to distance s. The specified value of total power P_(G)remains constant between the respective adjustments. The slight increasein specific power P_(S) that has occurred in the meantime can betolerated.

The no-load power P_(L) relevant for the control of the treatment deviceis updated via the measured distance.

A no-load power P_(L) is verified when fibrous material 1 is presentduring opening and/or closing of treatment nip 6 at normal operatingparameters, such as pressure, flow rate and stock consistency. Thisverification can be scheduled every 1-2 weeks, up to once daily.

For this purpose, the no-load power P_(L) of the treatment device ismeasured when the treatment nip is opened and/or closed, and it ischecked whether the assumed value of the no-load power P_(L) isconsistent with the measured value. As a result, a malfunction in thedistance measurement can also be reliably detected if the measured valueof the no-load power deviates clearly from the value stored for therespective distance.

Also, on start-up of the treatment device or when treatment tools 3, 4or their fillings are replaced, the no-load power P_(L) is measured whentreatment nip 6 is closed and is stored in the memory as a startingvalue for the controller.

The knowledge of the at least approximately real no-load power P_(L) notonly has an influence on the specific power and the corresponding totalpower to be regulated, but if a specified, minimum no-load power P_(L)is not reached a correspondingly high level of wear on treatment tools3, 4 can be concluded, making replacement of the latter necessary.Provision can also be made for informing the user if a predetermineddistance value is not met, so that the user can plan and prepare for animminently needed replacement of the refining fillings.

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

What is claimed is:
 1. A method for controlling a device for treating afibrous material, the method comprising the steps of: providing that thedevice includes a housing in which at least a first treatment tool and asecond treatment tool are arranged, the first treatment tool and thesecond treatment tool: being mounted on a first base plate and a secondbase plate respectively; having a rotationally symmetrical shape; beingarranged coaxially relative to each other in that the first treatmenttool and the second treatment tool rotate relative to one another abouta common axis; delimiting at least one treatment nip through which thefibrous material flows; and having respectively a first treatmentprofile and a second treatment profile facing toward the at least onetreatment nip; mounting at least one of the first base plate and thesecond base plate respectively of at least one of the first treatmenttool and the second treatment tool in an axially movable manner in orderto compensate for a wear of the first treatment profile and the secondtreatment profile; measuring a distance between the first base plate andthe second base plate respectively of the first treatment tool and thesecond treatment tool of the at least one treatment nip during anoperation of the device; and selecting a value of a total powerdepending on the distance between the first base plate and the secondbase plate of the at least one treatment nip.
 2. The method according toclaim 1, wherein the value of the total power is selected dependingsolely on the distance between the first base plate and the second baseplate of the at least one treatment nip.
 3. The method according toclaim 1, wherein the value of the total power is selected in conjunctionwith a plurality of additional values, depending on the distance betweenthe first base plate and the second base plate of the at least onetreatment nip.
 4. The method according to claim 1, wherein the value ofthe total power is adjusted at least when a change in the distancebetween the first base plate and the second base plate of the at leastone treatment nip of at least 1 mm is detected.
 5. The method accordingto claim 1, wherein the value of the total power is adjusted at aplurality of predetermined time intervals, which is at least every 1 to2 weeks, depending on the distance between the first base plate and thesecond base plate of the at least one treatment nip.
 6. The methodaccording to claim 1, wherein, after replacing at least one of the firsttreatment tool and the second treatment tool, a no-load power ismeasured and is stored in a memory as a starting value for a controlsystem.
 7. The method according to claim 6, wherein, for a desiredtreatment intensity, a relevant specific power of the device, whichresults from a difference between the total power and the no-load power,is kept constant over an operating period, taking into account achanging no-load power.
 8. The method according to claim 1, wherein,after replacing at least one of the first treatment tool and the secondtreatment tool, a no-load power is measured – when the at least onetreatment nip is closed – and is stored in a memory as a starting valuefor a control system.
 9. The method according to claim 1, wherein, indetermining the value of the total power depending on the distancebetween the first base plate and the second base plate of the at leastone treatment nip, a plurality of values are accessed.
 10. The methodaccording to claim 9, wherein the plurality of values are a plurality ofcharacteristic diagrams stored in a memory of a controller.
 11. Themethod according to claim 1, wherein the method is used in a refiner.12. The method according to claim 11, wherein the refiner is an LCrefiner.
 13. A device for treating a fibrous material, the devicecomprising: a first base plate; a second base plate; a first treatmenttool; a second treatment tool; a housing in which at least the firsttreatment tool and the second treatment tool are arranged, the firsttreatment tool and the second treatment tool: being mounted on a firstbase plate and a second base plate respectively; having a rotationallysymmetrical shape; being arranged coaxially relative to each other;rotating relative to one another about a common axi; delimiting at leastone treatment nip through which the fibrous material flows; and havingrespectively a first treatment profile and a second treatment profilefacing toward the at least one treatment nip, at least one of the firstbase plate and the second base plate respectively of at least one of thefirst treatment tool and the second treatment tool being mounted in anaxially movable manner in order to compensate for a wear of the firsttreatment profile and the second treatment profile; a sensor configuredfor determining a position of an axially movable one of at least one ofthe first treatment tool and the second treatment tool; and a memory, inwhich a characteristic diagram is stored, the characteristic diagramcontaining a dependency of a no-load power depending on a change in adistance between the first treatment tool and the second treatment tool.14. The device according to claim 13, wherein the device includes a wearindicator configured for treating the first treatment tool and thesecond treatment tool, wherein the device is configured for triggering asignal when a value associated with the signal falls below apredetermined distance value or a predetermined distance change.